Hi folks...

So I seem to be having an overheating issue. Truck was bone stock 5.2 Magnum/automatic when I bought it and it got hot on a long climb once. I've mostly been driving it the whopping 2 mile round trip to and from work. It's no longer totally stock, but the overheating is still a problem. Changes so far (not just for the cooling issue - bought it as a semi-project because my other cars don't add enough stress to my life):
* MSD multispark and coil, STI plug wires, new copper cap/rotor, Bosch copper plugs
* Radiator machine flush & fill + water wetter, new rad cap, new sever duty fan clutch, 180deg thermostat
* Transmission flush and fill
* Dynomax muffler

Truck runs beautifully, idles smooth, chirps the tires going into second, etc etc etc. Not losing any coolant and no smoke/steam from the tailpipe. There are some rusty looking flecks in the overflow tank and a little bit of milkshake only on the area above the pressure plate on the radiator cap. I'm starting to think I killed my head gasket - I will do a compression test next weekend (ran out of time this weekend), but anybody have any thoughts or suggestions?

Idling in 90deg with the a/c on, the temp gets freaky close to redline and freeway speed driving doesn't drop it. Only thing that does is downhill coasting.

 

Check to see that the thermostat is opening (do you see cross flow from the drivers side to the pax side when the engine is warmed up?) Check to see if the radiator is actually flowing--a machine flush won't do much if the passages are clogged. Do a pressure check. Probably the 'milk shake' is a bit of residual 'bars leak' left over from a previous owner.

My 96 was leaking coolant from the bypass hose (runs from the front of the plenum to the top of the water pump) and was seeping at the corners of the intake gaskets--both oil and coolant. Fortunately, none was leaking into the engine oil. If you need to do the intake gaskets, replace the valley pan (tin) with a Hughes Engine 1/4 aluminum plate one. RockAuto sells a very complete Dorman gasket set for about $25--includes all the gaskets, the bypass hose, a thermostat, valley pan bolts, and plenum bolts--all you need to add are new hose clamps and a lot of elbow grease. & maybe a thermostat housing and the heater tube that goes into the side of the waterpump--available from Autozone, O'reilly's, or Advanced.

While I had my 5.2 top end apart, I also replace all the hoses and the water pump. One does get rather deep in the engine to do these repairs, I'd hate to do it twice.

If you don't already have one, look for a Factory Service Manual. Don't bother with Haynes or Chilton--they're pretty generic and painfully worthless. I got mine for about $20 shipped on Ebay.

 

Thanks for the tips... Looking forward to the compression test. Not looking forward to tearing apart an engine, but I don't mind doing it. I have the FSM in digital form. Never met a Haynes I've liked, probably never will.

I'm reluctant to blame thermostat since I had similar symptoms with new and old 'stats... But then I remember my Jeep J2000 that got THREE bad starter motors in a row (all under warranty, thankfully).

Next weekend should be greasy... My students always make fun of me on Monday mornings when I show up all dressed up with black hands

 

Doing the intake manifold isn't that bad. The worst for me was those damn injectors. Buy new o-rings so replace the others, they can tear, then you leak fuel. It happened to me, FML.
But your problem sounds more like a water pump issue. But.... I have no idea how to check that.

 

I'm willing to bet it's a headgasket. And knowing these engines it's probably a cracked head if you got it hot, even once. I've seen lots of vehicles run and drive perfectly but overheat and it turns out to be a headgasket/cracked head. Bring it to a shop you trust and have them check it out.

 

A little tip for the injector o-rings; lube them up with a LIGHT coating of clean motor oil before you install the injectors. Just enough to make them glossy. Then when you install them, do not twist them in as this is prone to cutting the o-rings with the top shoulder of the sealing groove. Gently work them into the intake with light pressure while rotating the top of the injector in a small, circular motion. Get all of the injectors in one side and set the fuel rail on top of them, oiled, you can do the same thing again by grabbing the rail and moving the whole thing in the same circular motion. You may need to work from one end of the rail to the other to get them all seated. Any residual oil will run through the intake and get burned off, or mix with the fuel on the top side of the injector and go through that way. This also helps fight corrosion in the bungs on the intake as the oil will coat the aluminum. I would suggest you clean the bungs out with a small brass cone brush on a dremel tool ONLY if you have the intake off. You don't want to blast that crud down into your motor doing it with the intake on.

 

Oh injectors are always fun. I've replaced them in a few of my cars now... Twice in the Range Rover!

I guess we find out this weekend what's going on... What sort of compression numbers should I be looking for on a healthy 318? A quick search showed me the minimum is 100, but that seems mighty low to me.

 

100 is minimum. 170 is factory (or so Crazy 4x4 told me)

 

my friends camaro kept overheating after he bought it. we replaced all the hoses, water pump, heater core, and t-stat, eventually the radiator cracked and after replacing it(cheap plastic with cheap plastic) the car stopped over heating. also check the front of the radiator for corrosion i had that problem with my 93 which, as we did with my friends camaro, found was causing the problem

 

I find my 92 dak had some nasty build up on the outside. I power washed it and then blew it out with compressed air. It is so shiny and cool now. I also did a flush with a prestone kit. Just drive around for 4-8 hours and it was great.